2002 xboxes, i tried booting a copied dvd-r game and the xboxes reports invalid media, after loading the game (dashboard fades out, goes to black logo screen with the x)
i have tried this media on older xboxes with the beta enigmah chip and it works fine
are there any other reports of not working on april 11, 2002 xboxes?
also, the first time turning on the xbox with the modchip installed there was a beep on 2 of the 3 xboxes that i installed, but then after shutting down and turning back on it will start up

Try A-brand CD-RW's like Verbatim, Imation or TDK. if still no luck you could try the DVD-pot tweak which is described under tutorials...

Before you do that you could perhaps check if your chip is working by running a DVD movie and see if Macrovsion is switched off.